Angle-resolved Photoluminescence and Electroluminescence of LEDs and Light-Emitting Materials
/Developing next-generation display technologies or thin-film devices can be massively advanced with the help of cutting-edge instruments. All of our research tools have been developed with this ethos in mind. This is why we say that FLUXiM’s tools “Boost your R&D”. In this month’s news, we’re pleased to be sharing new research which has been enabled with the help of our unique spectrometer PHELOS.
About Phelos
Phelos is a gonio-spectrometer to characterize light-emitting devices and thin films over varied emission and polarization angles. While traditional instruments focus on either electroluminescence (EL) or photoluminescence (PL), Phelos is the only angular-resolved spectrometer that incorporates both El and PL in one table-top compact system. The software allows full control of your experiments and can be easily coupled to the powerful simulation software Setfos for data analysis, parameter extraction, and device modeling.
Contact us if you want to see a live demo of Phelos
- Organic LEDs - Perovskite LEDs
- Quantum Dot LEDs - QD-Films for LCDs - Micro-LEDs
New Results Obtained with Phelos
We’re passionate about R&D and making tools that enable great work. So it’s always a pleasure to read how our instruments are being used by our colleagues in research. Below you’ll find some recent results obtained with Phelos.
Optical Outcoupling Efficiency of Organic Light-Emitting Diodes with a Broad Recombination Profile
Yungui Li, Naresh B. Kotadiya, Bas van der Zee, Paul W. M. Blom, and Gert-Jan A. H. Wetzelaer
Adv. Optical Mater. 2021, 2001812, 1
doi/full/10.1002/adom.202001812
Although a broadened recombination zone is beneficial for the lifetime of organic light-emitting diodes (OLEDs), its effect on the optical outcoupling efficiency is unknown.
The authors analyzed the effect of a broad recombination zone in OLEDs – which is typically observed in polymer LEDs - on the optical outcoupling efficiency. Unlike previous investigations of the optical outcoupling of OLEDs, they couple the optical model with electrical simulations of the recombination profile, based on experimentally validated charge–transport parameters.
It is shown that the broadening of the recombination zone does not go at the expense of the optical outcoupling efficiency while retaining the benefits of a simplified architecture and enhanced operational stability.
As key model ingredients, they had to determine the dipole orientation in their emitter film. This was done by measuring the angle-dependent PL spectra of the EML with Phelos and fitting the angular dependence of photoluminescence with Setfos.
Their recombination profile and outcoupling efficiency analysis can be readily reproduced with Setfos emission and drift-diffusion module.
“Phelos angle-dependent photoluminescence (PL)/electroluminescence (EL) spectrometer along with Setfos package is a great combination of hardware and software to characterize the orientation of emission transition dipole moment. User-friendly interface and a broad range of parameters, such as polarization angles, position angles, driving current, and J-V parameters to investigate the PL as well as EL characteristics of light-emitting semiconductors. We have extensively used both Phelos and Setfos to understand the quantum emission characteristics of perovskites and organometallic complexes and light-extraction efficiency in PeLEDs and OLEDs. We found these tools allowed fast data acquisition, simulation, and in-depth understanding of emission characteristics of LEDs and OLEDs.”
Dr. Sudhir Kumar, Nanomaterials Engineering Research Group, Institute for Chemical and Bioengineering, ETH Zurich
Kinetic Control over Self-Assembly of Semiconductor Nanoplatelets
R. Momper, H. Zhang, S. Chen, H. Halim, E. Johannes, S. Yordanov, D. Braga, B. Blülle, D. Doblas, T. Kraus, M. Bonn, H. I. Wang, A. Riedinger
Nano Lett. 2020, 20, 6, 4102
doi/abs/10.1021/acs.nanolett.9b05270
Semiconductor nanoplatelets of CdSe exhibit spectrally pure fluorescence. By having the platelets collectively oriented in the solid-state is also possible to obtained polarized light emission from a monolayer. The main problem was to avoid adding insulating ligands that are surely helping alignment of the platelets but are making the film not interesting from the electrical point of view. This limitation has been resolved by the team lead by Dr. Riedinger at the Max-Planck Institute for Polymer Research.
The researchers controlled the collective nanoplatelets’ orientation in monolayers kinetically, by exploiting the solvent evaporation rate in self-assembly at liquid interfaces. The monolayer films with controlled nanoplatelets orientation exhibit long-range ordering of transition dipole moments and macroscopically polarized light emission. Moreover, the in-plane electronic coupling between nanoplatelets enables charge transport through a single nanoplatelets monolayer.
The authors performed angular and polarization-resolved PL measurements with Phelos and extract the dipole orientation by fitting the data with Setfos. Their analysis conclusively demonstrated that even at the millimeter scale the platelets maintain a long-range order (face-down or edge-up) and that their photoluminescence is polarized.
Fluxim's Phelos angular luminescence spectrometer is a powerful tool in our lab due to its versatility. In my daily work, I have used it so far in several research projects, e.g., to characterize light-coupling enhancement layers for OLEDs, to investigate the emission profile of quantum dot down-conversion layers, and, in combination with the Setfos simulation software, to determine the emission zone in multilayer phosphorescent or advanced TADF OLEDs.
Compared to our old, home-built angular emission measurement setup, what I like most about Phelos is its compact design, which allows me to use it in our glovebox system so that I can measure unencapsulated samples. Other advantages include the plug-and-play system via USB cable, the user-friendly software with individual measurement routines, and the easy positioning and contacting of samples thanks to the wide-opening doors, live camera image, and magnetic probe tips.
Dr. Markus Regnat, ZHAW School of Engineering, Switzerland
Scalable photonic sources using two-dimensional lead halide perovskite superlattices
J. Jagielski, S. F. Solari, L. Jordan, D. Scullion, B. Blülle, Y.-T. Li, F. Krumeich, Y.-C. Chiu, B. Ruhstaller, E. J. G. Santos, C.-J. Shih
Nature Communications 2020, 11, 387
doi.org/10.1038/s41467-019-14084-3
The authors are showing that miniaturized photonic sources based on semiconducting two-dimensional (2D) materials could offer new technological opportunities beyond the modern III-V systems.
They have been able to decouple multi-quantum-well superlattices comprised of colloidal quantum wells of lead halide perovskites with ultrathin quantum barriers. This is a unique demonstration of a scalable photonic source with 2D material superlattices with narrow-band emission, high quantum yield, enhanced light outcoupling, and wavelength tunability. These characteristics are highly desirable for many near-field and far-field applications such as nanoantennas and light-emitting diodes.
Phelos provided a unique advantage to these researchers for their angle-resolved PL analyses. Phelos is equipped with a hemispherical glass lens, which allowed the extraction of photons with a normalized wave vector k/k0 > 1, which are usually lost in substrate modes.
J-Aggregation Enhances the Electroluminescence Performance of a Sky-Blue Thermally Activated Delayed-Fluorescence Emitter in Nondoped OLEDs
Wei Li, Wenqi Li, Lin Gan, Mengke Li, Nan Zheng, Chengyun Ning, Dongcheng Chen, Yuan-Chun Wu, and Shi-Jian Su
ACS Appl. Mater. Interfaces 2020, 12, 2
https://pubs.acs.org/doi/pdf/10.1021/acsami.9b17585
The authors are presenting here a new thermally activated delayed-fluorescence (TADF) that exhibits enhanced electroluminescence in non-doped organic light-emitting diodes (OLEDs). A high external quantum efficiency (EQE) of 25.7% was achieved in a non-doped sky-blue TADF OLED, which is higher than any reported EQE value of nondoped sky-blue TADF OLEDs.
The paper describes in detail an efficient TADF-emitter, called DspiroAc-TRZ. Crystals of this molecule show a nonplanar packing pattern, which leads to highly efficient solid-state luminescence, short triplet exciton diffusion length, and tiny geometric vibrational relaxation in the excited state.
The dipole orientation of the different films was determined by measuring the PL of these systems with Phelos and fitting the data with Setfos.
Discover More Research Enabled by Phelos >
Contact us if you need more information about Phelos
LIGHT CONVERSION USING PEROVSKITE QUANTUM DOTS
Quantum dots are crystalline semiconductor particles, with a radius of few nanometers, whose optical and electrical properties are essentially determined by the size. The smaller the particles, the more the optical absorption and emission shift towards shorter wavelengths.
By far, the most important application for nanocrystals is quantum dot enhanced liquid crystal displays (LCDs). The most famous brands, are Sony Triluminous and Samsung QLED TVs. In these displays, quantum dots are used as down-converting materials to modify the background light to the desired color right before the color filters, or they are added to the light diffusor layers which uniformly distribute the background light over the whole display.
This blog post describes some of the properties and applications of quantum dots, in particular perovskite nanocrystals.
We show how to characterize quantum dot background scattering films using angular resolved electroluminescence (Phelos) and analyze the results with a fully coupled electro-optical simulation (Setfos).
You can read the full blog here >
Phelos Operation Modes
Phelos is equipped with an internal Source Measurement Unit (SMU) that is used for both the EL or PL characterization.
Electroluminescence
Photoluminescence
Down-Conversion & Scattering
You can download our detailed presentation of Phelos here
Post-processing of Experimental Data:
Working point
Efficacy (cd/A)
CIE coordinates
Color temperature, CRI …
Spectral Irradiance/Intensity
Radiance/Radiant Intensity
Luminous Intensity
The software provided with Phelos is an all-in-one platform to characterize your sample and analyze your data. The Graphical User Interface (GUI) allows you to extract easily the orientation of the dipoles in your light-emitting film with an automated fitting routine.
Phelos Advantages:
Angular photoluminescence (PL) spectroscopy on organic, quantum-dot, and perovskite light-emitting thin films.
Angular electroluminescence (EL) spectroscopy on OLEDs and other light-emitting devices.
Angle dependence of the light emission of an OLED and other light-emitting devices.
Compatible with top and bottom emitting OLED structures.
Detection of p- and s-polarized signal, or continuous sweep over polarization angles.
Determine where in your emission layer the dipoles are emitting, and which is the orientation of the dipoles.
Integrated data analysis allows you to determine dipole orientation with one click.
Easily coupled to Setfos for advanced parameter extraction and device modeling.
Flexible contacting of any sample geometry and easy sample alignment.
Acquire current-voltage-luminance (IVL) curves with the integrated SMU
Measure: EQE, lm/W, Cd/A, CRI, and CIE coordinates
Polarizers and macro-extraction lens included. Multiple light sources are available.
Phelos is CE certified.
